Method and apparatus for enhancing discontinuous reception procedure in wireless communication system to which for carrier aggregation scheme is applied

ABSTRACT

The present invention relates to a method for receiving a Physical Downlink Control Channel (PDCCH) by a user equipment (UE) in a wireless communication system to which a carrier aggregation scheme is applied. In particular, the method includes the steps of: monitoring the PDCCH during an On Duration within a discontinuous reception (DRX) cycle on a specific serving cell among at least two activated serving cells, and monitoring the PDCCH during an Active Time within the DRX cycle on all of the at least two serving cells based on the PDCCH being detected during the On Duration within the DRX cycle on the specific serving cell.

The frame structure illustrated in FIG. 5 is purely exemplary and thenumber of subframes, the number of slots, and/or the number of symbolsin a frame may be variously changed. In the 3GPP based wirelesscommunication system, OFDM numerologies (e.g., subcarrier spacing (SCS),transmission time interval (TTI) duration) may be differently configuredbetween a plurality of cells aggregated for one UE. For example, if a UEis configured with different SCSs for cells aggregated for the cell, an(absolute time) duration of a time resource (e.g. a subframe, a slot, ora TTI) including the same number of symbols may be different among theaggregated cells. Herein, symbols may include OFDM symbols (or CP-OFDMsymbols), SC-FDMA symbols (or discrete Fourier transform-spread-OFDM(DFT-s-OFDM) symbols).

Referring to FIG. 5, downlink and uplink transmissions are organizedinto frames. Each frame has T_(f)=10 ms duration. Each frame is dividedinto two half-frames, where each of the half-frames has 5 ms duration.Each half-frame consists of 5 subframes, where the duration T_(sf) persubframe is 1 ms. Each subframe is divided into slots and the number ofslots in a subframe depends on a subcarrier spacing. Each slot includes14 or 12 OFDM symbols based on a cyclic prefix (CP). In a normal CP,each slot includes 14 OFDM symbols and, in an extended CP, each slotincludes 12 OFDM symbols. The numerology is based on exponentiallyscalable subcarrier spacing Δf=2^(u)*15 kHz. The following table showsthe number of OFDM symbols per slot, the number of slots per frame, andthe number of slots per for the normal CP, according to the subcarrierspacing Δf=2^(u)*15 kHz.

TABLE 1 u N^(slot) _(symb) N^(frame, u) _(slot) N^(subframe, u) _(slot)0 14 10 1 1 14 20 2 2 14 40 4 3 14 80 8 4 14 160 16

The following table shows the number of OFDM symbols per slot, thenumber of slots per frame, and the number of slots per for the extendedCP, according to the subcarrier spacing Δf=2u*15 kHz.

TABLE 2 u N^(slot) _(symb) N^(frame, u) _(slot) N^(subframe, u) _(slot)2 12 40 4

A slot includes plural symbols (e.g., 14 or 12 symbols) in the timedomain. For each numerology (e.g. subcarrier spacing) and carrier, aresource grid of N^(size,u) _(grid,x)*N^(RB) _(sc) subcarriers andN^(subframe,u) _(symb) OFDM symbols is defined, starting at commonresource block (CRB) N^(start,u) _(grid) indicated by higher-layersignaling (e.g. radio resource control (RRC) signaling), whereN^(size,u) _(grid,x) is the number of resource blocks in the resourcegrid and the subscript x is DL for downlink and UL for uplink. N^(RB)_(sc) is the number of subcarriers per resource blocks. In the 3GPPbased wireless communication system, N^(RB) _(sc) is 12 generally. Thereis one resource grid for a given antenna port p, subcarrier spacingconfiguration u, and transmission direction (DL or UL). The carrierbandwidth N^(size,u) _(grid) for subcarrier spacing configuration u isgiven by the higher-layer parameter (e.g. RRC parameter). Each elementin the resource grid for the antenna port p and the subcarrier spacingconfiguration u is referred to as a resource element (RE) and onecomplex symbol may be mapped to each RE. Each RE in the resource grid isuniquely identified by an index k in the frequency domain and an index lrepresenting a symbol location relative to a reference point in the timedomain. In the 3GPP based wireless communication system, a resourceblock is defined by 12 consecutive subcarriers in the frequency domain.

In the 3GPP NR system, resource blocks are classified into CRBs andphysical resource blocks (PRBs). CRBs are numbered from 0 and upwards inthe frequency domain for subcarrier spacing configuration u. The centerof subcarrier 0 of CRB 0 for subcarrier spacing configuration ucoincides with ‘point A’ which serves as a common reference point forresource block grids. In the 3GPP NR system, PRBs are defined within abandwidth part (BWP) and numbered from 0 to N^(size) _(BWP,i)-1, where iis the number of the bandwidth part. The relation between the physicalresource block n_(PRB) in the bandwidth part i and the common resourceblock n_(CRB) is as follows: n_(CRB)=n_(CRB)+N^(size) _(BWP,i), whereN^(size) _(BWP,i) is the common resource block where bandwidth partstarts relative to CRB 0. The BWP includes a plurality of consecutiveresource blocks. A carrier may include a maximum of N (e.g., 5) BWPs. AUE may be configured with one or more BWPs on a given component carrier.Only one BWP among BWPs configured to the UE can active at a time. Theactive BWP defines the UE's operating bandwidth within the cell'soperating bandwidth.

NR frequency bands are defined as 2 types of frequency range, FR1 andFR2. FR2 is may also called millimeter wave(mmW). The frequency rangesin which NR can operate are identified as described in Table 3.

TABLE 3 Frequency Range Corresponding designation frequency rangeSubcarrier Spacing FR1  450 MHz-7125 MHz  15, 30, 60 kHz FR2 24250MHz-52600 MHz 60, 120, 240 kHz

FIG. 6 illustrates a data flow example in the 3GPP NR system.

In FIG. 6, “RB” denotes a radio bearer, and “H” denotes a header. Radiobearers are categorized into two groups: data radio bearers (DRB) foruser plane data and signaling radio bearers (SRB) for control planedata. The MAC PDU is transmitted/received using radio resources throughthe PHY layer to/from an external device. The MAC PDU arrives to the PHYlayer in the form of a transport block.

In the PHY layer, the uplink transport channels UL-SCH and RACH aremapped to physical uplink shared channel (PUSCH) and physical randomaccess channel (PRACH), respectively, and the downlink transportchannels DL-SCH, BCH and PCH are mapped to physical downlink sharedchannel (PDSCH), physical broad cast channel (PBCH) and PDSCH,respectively. In the PHY layer, uplink control information (UCI) ismapped to PUCCH, and downlink control information (DCI) is mapped toPDCCH. A MAC PDU related to UL-SCH is transmitted by a UE via a PUSCHbased on an UL grant, and a MAC PDU related to DL-SCH is transmitted bya BS via a PDSCH based on a DL assignment.

In order to transmit data unit(s) of the present disclosure on UL-SCH, aUE shall have uplink resources available to the UE. In order to receivedata unit(s) of the present disclosure on DL-SCH, a UE shall havedownlink resources available to the UE. The resource allocation includestime domain resource allocation and frequency domain resourceallocation. In the present disclosure, uplink resource allocation isalso referred to as uplink grant, and downlink resource allocation isalso referred to as downlink assignment. An uplink grant is eitherreceived by the UE dynamically on PDCCH, in a Random Access Response, orconfigured to the UE semi-persistently by RRC. Downlink assignment iseither received by the UE dynamically on the PDCCH, or configured to theUE semi-persistently by RRC signaling from the BS.

In UL, the BS can dynamically allocate resources to UEs via the CellRadio Network Temporary Identifier (C-RNTI) on PDCCH(s). A UE alwaysmonitors the PDCCH(s) in order to find possible grants for uplinktransmission when its downlink reception is enabled (activity governedby discontinuous reception (DRX) when configured). In addition, withConfigured Grants, the BS can allocate uplink resources for the initialHARQ transmissions to UEs. Two types of configured uplink grants aredefined: Type 1 and Type 2. With Type 1, RRC directly provides theconfigured uplink grant (including the periodicity). With Type 2, RRCdefines the periodicity of the configured uplink grant while PDCCHaddressed to Configured Scheduling RNTI (CS-RNTI) can either signal andactivate the configured uplink grant, or deactivate it; i.e. a PDCCHaddressed to CS-RNTI indicates that the uplink grant can be implicitlyreused according to the periodicity defined by RRC, until deactivated.

In DL, the BS can dynamically allocate resources to UEs via the C-RNTIon PDCCH(s). A UE always monitors the PDCCH(s) in order to find possibleassignments when its downlink reception is enabled (activity governed byDRX when configured). In addition, with Semi-Persistent Scheduling(SPS), the BS can allocate downlink resources for the initial HARQtransmissions to UEs: RRC defines the periodicity of the configureddownlink assignments while PDCCH addressed to CS-RNTI can either signaland activate the configured downlink assignment, or deactivate it. Inother words, a PDCCH addressed to CS-RNTI indicates that the downlinkassignment can be implicitly reused according to the periodicity definedby RRC, until deactivated.

<Resource Allocation by PDCCH (i.e. Resource Allocation by DCI)>

PDCCH can be used to schedule DL transmissions on PDSCH and ULtransmissions on PUSCH, where the downlink control information (DCI) onPDCCH includes: downlink assignments containing at least modulation andcoding format (e.g., modulation and coding scheme (MCS) index IMCS),resource allocation, and hybrid-ARQ information related to DL-SCH; oruplink scheduling grants containing at least modulation and codingformat, resource allocation, and hybrid-ARQ information related toUL-SCH. The size and usage of the DCI carried by one PDCCH are varieddepending on DCI formats. For example, in the 3GPP NR system, DCI format0_0 or DCI format 0_1 is used for scheduling of PUSCH in one cell, andDCI format 1_0 or DCI format 1_1 is used for scheduling of PDSCH in onecell.

FIG. 7 illustrates an example of PDSCH time domain resource allocationby PDCCH, and an example of PUSCH time resource allocation by PDCCH.

Downlink control information (DCI) carried by a PDCCH for schedulingPDSCH or PUSCH includes a value m for a row index m+1 to an allocationtable for PDSCH or PUSCH. Either a predefined default PDSCH time domainallocation A, B or C is applied as the allocation table for PDSCH, orRRC configured pdsch-TimeDomainAllocationList is applied as theallocation table for PDSCH. Either a predefined default PUSCH timedomain allocation A is applied as the allocation table for PUSCH, or theRRC configured pusch-TimeDomainAllocationList is applied as theallocation table for PUSCH. Which PDSCH time domain resource allocationconfiguration to apply and which PUSCH time domain resource allocationtable to apply are determined according to a fixed/predefined rule (e.g.Table 5.1.2.1.1-1 in 3GPP TS 38.214 v15.3.0, Table 6.1.2.1.1-1 in 3GPPTS 38.214 v15.3.0).

Each indexed row in PDSCH time domain allocation configurations definesthe slot offset K₀, the start and length indicator SLIV, or directly thestart symbol S and the allocation length L, and the PDSCH mapping typeto be assumed in the PDSCH reception. Each indexed row in PUSCH timedomain allocation configurations defines the slot offset K₂, the startand length indicator SLIV, or directly the start symbol S and theallocation length L, and the PUSCH mapping type to be assumed in thePUSCH reception. K₀ for PDSCH, or K₂ for PUSCH is the timing differencebetween a slot with a PDCCH and a slot with PDSCH or PUSCH correspondingto the PDCCH. SLIV is a joint indication of starting symbol S relativeto the start of the slot with PDSCH or PUSCH, and the number L ofconsecutive symbols counting from the symbol S. For PDSCH/PUSCH mappingtype, there are two mapping types: one is Mapping Type A wheredemodulation reference signal (DMRS) is positioned in 3^(rd) or 4^(th)symbol of a slot depending on the RRC signaling, and other one isMapping Type B where DMRS is positioned in the first allocated symbol.

The scheduling DCI includes the Frequency domain resource assignmentfield which provides assignment information on resource blocks used forPDSCH or PUSCH. For example, the Frequency domain resource assignmentfield may provide a UE with information on a cell for PDSCH or PUSCHtransmission, information on a bandwidth part for PDSCH or PUSCHtransmission, information on resource blocks for PDSCH or PUSCHtransmission.

<Resource Allocation by RRC>

As mentioned above, in uplink, there are two types of transmissionwithout dynamic grant: configured grant Type 1 where an uplink grant isprovided by RRC, and stored as configured grant; and configured grantType 2 where an uplink grant is provided by PDCCH, and stored or clearedas configured uplink grant based on L1 signaling indicating configureduplink grant activation or deactivation. Type 1 and Type 2 areconfigured by RRC per serving cell and per BWP. Multiple configurationscan be active simultaneously only on different serving cells. For Type2, activation and deactivation are independent among the serving cells.For the same serving cell, the MAC entity is configured with either Type1 or Type 2.

A UE is provided with at least the following parameters via RRCsignaling from a BS when the configured grant type 1 is configured:

-   -   cs-RNTI which is CS-RNTI for retransmission;    -   periodicity which provides periodicity of the configured grant        Type 1;    -   timeDomainOffset which represents offset of a resource with        respect to SFN=0 in time domain;    -   timeDomainAllocation value m which provides a row index m+1        pointing to an allocation table, indicating a combination of a        start symbol S and length L and PUSCH mapping type;    -   frequencyDomainAllocation which provides frequency domain        resource allocation; and    -   mcsAndTBS which provides IMCS representing the modulation order,        target code rate and transport block size. Upon configuration of        a configured grant Type 1 for a serving cell by RRC, the UE        stores the uplink grant provided by RRC as a configured uplink        grant for the indicated serving cell, and 36nitialize or        re-initialize the configured uplink grant to start in the symbol        according to timeDomainOffset and S (derived from SLIV), and to        reoccur with periodicity. After an uplink grant is configured        for a configured grant Type 1, the UE considers that the uplink        grant recurs associated with each symbol for which:        [(SFN*numberOfSlotsPerFrame (numberOfSymbolsPerSlot)+(slot        number in the frame×numberOfSymbolsPerSlot)+symbol number in the        slot]=(timeDomainOffset*numberOfSymbolsPerSlot+S+N*periodicity)        modulo (1024*numberOfSlotsPerFrame*numberOfSymbolsPerSlot), for        all N>=0.

A UE is provided with at least the following parameters via RRCsignaling from a BS when the configured gran Type 2 is configured:

-   -   cs-RNTI which is CS-RNTI for activation, deactivation, and        retransmission; and    -   periodicity which provides periodicity of the configured grant        Type 2. The actual uplink grant is provided to the UE by the        PDCCH (addressed to CS-RNTI). After an uplink grant is        configured for a configured grant Type 2, the UE considers that        the uplink grant recurs associated with each symbol for which:        [(SFN*numberOfSlotsPerFrame*numberOfSymbolsPerSlot)+(slot number        in the frame*numberOfSymbolsPerSlot)+symbol number in the        slot]=[(SFN_(start time)*numberOfSlotsPerFrame*numberOfSymbolsPerSlot+slot_(start time)*numberOfSymbolsPerSlot+symbol_(start time))+N*periodicity]modulo        (1024×numberOfSlotsPerFrame*numberOfSymbolsPerSlot), for all        N>=0, where SFN_(start time), slot_(start time), and        symbol_(start time) are the SFN, slot, and symbol, respectively,        of the first transmission opportunity of PUSCH where the        configured uplink grant was (re-)initialized.        numberOfSlotsPerFrame and numberOfSymbolsPerSlot refer to the        number of consecutive slots per frame and the number of        consecutive OFDM symbols per slot, respectively (see Table 1 and        Table 1).

For configured uplink grants, the HARQ Process ID associated with thefirst symbol of a UL transmission is derived from the followingequation:

HARQ Process ID=[floor(CURRENT_symbol/periodicity)]modulonrofHARQ-Processes

whereCURRENT_symbol=(SFN×numberOfSlotsPerFrame×numberOfSymbolsPerSlot+slotnumber in the frame×numberOfSymbolsPerSlot+symbol number in the slot),and numberOfSlotsPerFrame and numberOfSymbolsPerSlot refer to the numberof consecutive slots per frame and the number of consecutive symbols perslot, respectively as specified in TS 38.211. CURRENT_symbol refers tothe symbol index of the first transmission occasion of a repetitionbundle that takes place. A HARQ process is configured for a configureduplink grant if the configured uplink grant is activated and theassociated HARQ process ID is less than nrofHARQ-Processes.

For downlink, a UE may be configured with semi-persistent scheduling(SPS) per serving cell and per BWP by RRC signaling from a BS. Multipleconfigurations can be active simultaneously only on different servingcells. Activation and deactivation of the DL SPS are independent amongthe serving cells. For DL SPS, a DL assignment is provided to the UE byPDCCH, and stored or cleared based on L1 signaling indicating SPSactivation or deactivation. A UE is provided with the followingparameters via RRC signaling from a BS when SPS is configured:

-   -   cs-RNTI which is CS-RNTI for activation, deactivation, and        retransmission;    -   nrofHARQ-Processes: which provides the number of configured HARQ        processes for SPS;    -   periodicity which provides periodicity of configured downlink        assignment for SPS.

When SPS is released by upper layers, all the correspondingconfigurations shall be released.

After a downlink assignment is configured for SPS, the UE considerssequentially that the N^(th) downlink assignment occurs in the slot forwhich: (numberOfSlotsPerFrame*SFN+slot number in theframe)=[(numberOfSlotsPerFrame*SFN_(start time)+slot_(start time))+N*periodicity*numberOfSlotsPerFrame/10]modulo(1024*numberOfSlotsPerFrame), where SFN_(start time) andslot_(start time) are the SFN and slot, respectively, of the firsttransmission of PDSCH where the configured downlink assignment was(re-)initialized.

For configured downlink assignments, the HARQ Process ID associated withthe slot where the DL transmission starts is derived from the followingequation:

HARQ  Process  ID = [floor  (CURRENT_slot × 10/(numberOfSlotsPerFrame × periodicity))]  modulo  nrofHARQ-Processes

where CURRENT_slot=[(SFN×numberOfSlotsPerFrame)+slot number in theframe] and numberOfSlotsPerFrame refers to the number of consecutiveslots per frame as specified in TS 38.211.

A UE validates, for scheduling activation or scheduling release, a DLSPS assignment PDCCH or configured UL grant type 2 PDCCH if the cyclicredundancy check (CRC) of a corresponding DCI format is scrambled withCS-RNTI provided by the RRC parameter cs-RNTI and the new data indicatorfield for the enabled transport block is set to 0. Validation of the DCIformat is achieved if all fields for the DCI format are set according toTable 4 or Table 5. Table 4 shows special fields for DL SPS and UL grantType 2 scheduling activation PDCCH validation, and Table 5 shows specialfields for DL SPS and UL grant Type 2 scheduling release PDCCHvalidation.

TABLE 4 DCI format 0_0/0_1 DCI format 1_0 DCI format 1_1 HARQ processset to all ‘0’s set to all ‘0’s set to all ‘0’s number Redundancy set to‘00’ set to ‘00’ For the enabled version transport block: set to ‘00’

TABLE 5 DCI format 0_0 DCI format 1_0 HARQ process number set to all‘0’s set to all ‘0’s Redundancy version set to ‘00’ set to ‘00’Modulation and coding set to all ‘1’s set to all ‘1’s scheme Resourceblock set to all ‘1’s set to all ‘1’s assignment

Actual DL assignment and actual UL grant, and the correspondingmodulation and coding scheme are provided by the resource assignmentfields (e.g. time domain resource assignment field which provides Timedomain resource assignment value m, frequency domain resource assignmentfield which provides the frequency resource block allocation, modulationand coding scheme field) in the DCI format carried by the DL SPS and ULgrant Type 2 scheduling activation PDCCH. If validation is achieved, theUE considers the information in the DCI format as valid activation orvalid release of DL SPS or configured UL grant Type 2.

For UL, the processor(s) 102 of the present disclosure may transmit (orcontrol the transceiver(s) 106 to transmit) the data unit of the presentdisclosure based on the UL grant available to the UE. The processor(s)202 of the present disclosure may receive (or control the transceiver(s)206 to receive) the data unit of the present disclosure based on the ULgrant available to the UE.

For DL, the processor(s) 102 of the present disclosure may receive (orcontrol the transceiver(s) 106 to receive) DL data of the presentdisclosure based on the DL assignment available to the UE. Theprocessor(s) 202 of the present disclosure may transmit (or control thetransceiver(s) 206 to transmit) DL data of the present disclosure basedon the DL assignment available to the UE.

The data unit(s) of the present disclosure is(are) subject to thephysical layer processing at a transmitting side before transmission viaradio interface, and the radio signals carrying the data unit(s) of thepresent disclosure are subject to the physical layer processing at areceiving side. For example, a MAC PDU including the PDCP PDU accordingto the present disclosure may be subject to the physical layerprocessing as follows.

FIG. 8 illustrates an example of physical layer processing at atransmitting side.

The following tables show the mapping of the transport channels (TrCHs)and control information to its corresponding physical channels. Inparticular, Table 6 specifies the mapping of the uplink transportchannels to their corresponding physical channels, Table 7 specifies themapping of the uplink control channel information to its correspondingphysical channel, Table 8 specifies the mapping of the downlinktransport channels to their corresponding physical channels, and Table 9specifies the mapping of the downlink control channel information to itscorresponding physical channel.

TABLE 6 TrCH Physical Channel UL-SCH PUSCH RACH PRACH

TABLE 7 Control information Physical Channel UCI PUCCH, PUSCH

TABLE 8 TrCH Physical Channel DL-SCH PDSCH BCH PBCH PCH PDSCH

TABLE 9 Control information Physical Channel DCI PDCCH

<Encoding>

Data and control streams from/to MAC layer are encoded to offertransport and control services over the radio transmission link in thePHY layer. For example, a transport block from MAC layer is encoded intoa codeword at a transmitting side. Channel coding scheme is acombination of error detection, error correcting, rate matching,interleaving and transport channel or control information mappingonto/splitting from physical channels.

In the 3GPP NR system, following channel coding schemes are used for thedifferent types of TrCH and the different control information types.

TABLE 10 TrCH Coding scheme UL-SCH LDPC DL-SCH PCH BCH Polar code

TABLE 11 Control Information Coding scheme DCI Polar code UCI Block codePolar code

For transmission of a DL transport block (i.e. a DL MAC PDU) or a ULtransport block (i.e. a UL MAC PDU), a transport block CRC sequence isattached to provide error detection for a receiving side. In the 3GPP NRsystem, the communication device uses low density parity check (LDPC)codes in encoding/decoding UL-SCH and DL-SCH. The 3GPP NR systemsupports two LDPC base graphs (i.e. two LDPC base matrixes): LDPC basegraph 1 optimized for small transport blocks and LDPC base graph 2 forlarger transport blocks. Either LDPC base graph 1 or 2 is selected basedon the size of the transport block and coding rate R. The coding rate Ris indicated by the modulation coding scheme (MCS) index IMCS. The MCSindex is dynamically provided to a UE by PDCCH scheduling PUSCH orPDSCH, provided to a UE by PDCCH activating or (re-)initializing the ULconfigured grant 2 or DL SPS, or provided to a UE by RRC signalingrelated to the UL configured grant Type 1. If the CRC attached transportblock is larger than the maximum code block size for the selected LDPCbase graph, the CRC attached transport block may be segmented into codeblocks, and an additional CRC sequence is attached to each code block.The maximum code block sizes for the LDPC base graph 1 and the LDPC basegraph 2 are 8448 bits and 3480 bits, respectively. If the CRC attachedtransport block is not larger than the maximum code block size for theselected LDPC base graph, the CRC attached transport block is encodedwith the selected LDPC base graph. Each code block of the transportblock is encoded with the selected LDPC base graph. The LDPC codedblocks are then individually rat matched. Code block concatenation isperformed to create a codeword for transmission on PDSCH or PUSCH. ForPDSCH, up to 2 codewords (i.e. up to 2 transport blocks) can betransmitted simultaneously on the PDSCH. PUSCH can be used fortransmission of UL-SCH data and layer 1/2 control information. Althoughnot shown in FIG. 8, the layer 1/2 control information may bemultiplexed with the codeword for UL-SCH data.

<Scrambling and Modulation>

The bits of the codeword are scrambled and modulated to generate a blockof complex-valued modulation symbols.

<Layer Mapping>

The complex-valued modulation symbols of the codeword are mapped to oneor more multiple input multiple output (MIMO) layers. A codeword can bemapped to up to 4 layers. A PDSCH can carry two codewords, and thus aPDSCH can support up to 8-layer transmission. A PUSCH supports a singlecodeword, and thus a PUSCH can support up to 4-layer transmission.

<Transform Precoding>

The DL transmission waveform is conventional OFDM using a cyclic prefix(CP). For DL, transform precoding (in other words, discrete Fouriertransform (DFT)) is not applied.

The UL transmission waveform is conventional OFDM using a CP with atransform precoding function performing DFT spreading that can bedisabled or enabled. In the 3GPP NR system, for UL, the transformprecoding can be optionally applied if enabled. The transform precodingis to spread UL data in a special way to reduce peak-to-average powerratio (PAPR) of the waveform. The transform precoding is a form of DFT.In other words, the 3GPP NR system supports two options for UL waveform:one is CP-OFDM (same as DL waveform) and the other one is DFT-s-OFDM.Whether a UE has to use CP-OFDM or DFT-s-OFDM is configured by a BS viaRRC parameters.

<Subcarrier Mapping>

The layers are mapped to antenna ports. In DL, for the layers to antennaports mapping, a transparent manner (non-codebook based) mapping issupported and how beamforming or MIMO precoding is performed istransparent to the UE. In UL, for the layers to antenna ports mapping,both the non-codebook based mapping and a codebook based mapping aresupported.

For each antenna port (i.e. layer) used for transmission of the physicalchannel (e.g. PDSCH, PUSCH), the complex-valued modulation symbols aremapped to subcarriers in resource blocks allocated to the physicalchannel.

<OFDM Modulation>

The communication device at the transmitting side generates atime-continuous OFDM baseband signal on antenna port p and subcarrierspacing configuration u for OFDM symbol 1 in a TTI for a physicalchannel by adding a cyclic prefix (CP) and performing IFFT. For example,for each OFDM symbol, the communication device at the transmitting sidemay perform inverse fast Fourier transform (IFFT) on the complex-valuedmodulation symbols mapped to resource blocks in the corresponding OFDMsymbol and add a CP to the IFFT-ed signal to generate the OFDM basebandsignal.

<Up-Conversion>

The communication device at the transmitting side up-convers the OFDMbaseband signal for antenna port p, subcarrier spacing configuration uand OFDM symbol l to a carrier frequency f₀ of a cell to which thephysical channel is assigned.

The processors 102 and 202 in FIG. 2 may be configured to performencoding, schrambling, modulation, layer mapping, transform precoding(for UL), subcarrier mapping, and OFDM modulation. The processors 102and 202 may control the transceivers 106 and 206 connected to theprocessors 102 and 202 to up-convert the OFDM baseband signal onto thecarrier frequency to generate radio frequency (RF) signals. The radiofrequency signals are transmitted through antennas 108 and 208 to anexternal device.

FIG. 9 illustrates an example of physical layer processing at areceiving side.

The physical layer processing at the receiving side is basically theinverse processing of the physical layer processing at the transmittingside.

<Frequency Down-Conversion>

The communication device at a receiving side receives RF signals at acarrier frequency through antennas. The transceivers 106 and 206receiving the RF signals at the carrier frequency down-converts thecarrier frequency of the RF signals into the baseband in order to obtainOFDM baseband signals.

<OFDM Demodulation>

The communication device at the receiving side obtains complex-valuedmodulation symbols via CP detachment and FFT. For example, for each OFDMsymbol, the communication device at the receiving side removes a CP fromthe OFDM baseband signals and performs FFT on the CP-removed OFDMbaseband signals to obtain complex-valued modulation symbols for antennaport p, subcarrier spacing u and OFDM symbol 1.

<Subcarrier Demapping>

The subcarrier demapping is performed on the complex-valued modulationsymbols to obtain complex-valued modulation symbols of a correspondingphysical channel. For example, the processor(s) 102 may obtaincomplex-valued modulation symbols mapped to subcarriers belong to PDSCHfrom among complex-valued modulation symbols received in a bandwidthpart. For another example, the processor(s) 202 may obtaincomplex-valued modulation symbols mapped to subcarriers belong to PUSCHfrom among complex-valued modulation symbols received in a bandwidthpart.

<Transform De-Precoding>

Transform de-precoding (e.g. IDFT) is performed on the complex-valuedmodulation symbols of the uplink physical channel if the transformprecoding has been enabled for the uplink physical channel. For thedownlink physical channel and for the uplink physical channel for whichthe transform precoding has been disabled, the transform de-precoding isnot performed.

<Layer Demapping>

The complex-valued modulation symbols are de-mapped into one or twocodewords.

<Demodulation and Descrambling>

The complex-valued modulation symbols of a codeword are demodulated anddescrambled into bits of the codeword.

<Decoding>

The codeword is decoded into a transport block. For UL-SCH and DL-SCH,either LDPC base graph 1 or 2 is selected based on the size of thetransport block and coding rate R. The codeword may include one ormultiple coded blocks. Each coded block is decoded with the selectedLDPC base graph into a CRC-attached code block or CRC-attached transportblock. If code block segmentation was performed on a CRC-attachedtransport block at the transmitting side, a CRC sequence is removed fromeach of CRC-attached code blocks, whereby code blocks are obtained. Thecode blocks are concatenated into a CRC-attached transport block. Thetransport block CRC sequence is removed from the CRC-attached transportblock, whereby the transport block is obtained. The transport block isdelivered to the MAC layer.

In the above described physical layer processing at the transmitting andreceiving sides, the time and frequency domain resources (e.g. OFDMsymbol, subcarriers, carrier frequency) related to subcarrier mapping,OFDM modulation and frequency up/down conversion can be determined basedon the resource allocation (e.g., UL grant, DL assignment).

For uplink data transmission, the processor(s) 102 of the presentdisclosure may apply (or control the transceiver(s) 106 to apply) theabove described physical layer processing of the transmitting side tothe data unit of the present disclosure to transmit the data unitwirelessly. For downlink data reception, the processor(s) 102 of thepresent disclosure may apply (or control the transceiver(s) 106 toapply) the above described physical layer processing of the receivingside to received radio signals to obtain the data unit of the presentdisclosure.

For downlink data transmission, the processor(s) 202 of the presentdisclosure may apply (or control the transceiver(s) 206 to apply) theabove described physical layer processing of the transmitting side tothe data unit of the present disclosure to transmit the data unitwirelessly. For uplink data reception, the processor(s) 202 of thepresent disclosure may apply (or control the transceiver(s) 206 toapply) the above described physical layer processing of the receivingside to received radio signals to obtain the data unit of the presentdisclosure.

FIG. 10 illustrates operations of the wireless devices based on theimplementations of the present disclosure.

The first wireless device 100 of FIG. 2 may generate firstinformation/signals according to the functions, procedures, and/ormethods described in the present disclosure, and then transmit radiosignals including the first information/signals wirelessly to the secondwireless device 200 of FIG. 2 (S10). The first information/signals mayinclude the data unit(s) (e.g. PDU, SDU, RRC message) of the presentdisclosure. The first wireless device 100 may receive radio signalsincluding second information/signals from the second wireless device 200(S30), and then perform operations based on or according to the secondinformation/signals (S50). The second information/signals may betransmitted by the second wireless device 200 to the first wirelessdevice 100 in response to the first information/signals. The secondinformation/signals may include the data unit(s) (e.g. PDU, SDU, RRCmessage) of the present disclosure. The first information/signals mayinclude contents request information, and the second information/signalsmay include contents specific to the usage of the first wireless device100. Some examples of operations specific to the usages of the wirelessdevices 100 and 200 will be described below.

In some scenarios, the first wireless device 100 may be a hand-helddevice 100 d of FIG. 1, which performs the functions, procedures, and/ormethods described in the present disclosure. The hand-held device 100 dmay acquire information/signals (e.g., touch, text, voice, images, orvideo) input by a user, and convert the acquired information/signalsinto the first information/signals. The hand-held devices 100 d maytransmit the first information/signals to the second wireless device 200(S10). The second wireless device 200 may be any one of the wirelessdevices 100 a to 100 f in FIG. 1 or a BS. The hand-held device 100 d mayreceive the second information/signals from the second wireless device200 (S30), and perform operations based on the secondinformation/signals (S50). For example, the hand-held device 100 d mayoutput the contents of the second information/signals to the user (e.g.in the form of text, voice, images, video, or haptic) through the I/Ounit of the hand-held device 100 d.

In some scenarios, the first wireless device 100 may be a vehicle or anautonomous driving vehicle 100 b, which performs the functions,procedures, and/or methods described in the present disclosure. Thevehicle 100 b may transmit (S10) and receive (S30) signals (e.g. dataand control signals) to and from external devices such as othervehicles, BSs (e.g. gNBs and road side units), and servers, through itscommunication unit (e.g. communication unit 110 of FIG. 1C). The vehicle100 b may include a driving unit, and the driving unit may cause thevehicle 100 b to drive on a road. The driving unit of the vehicle 100 bmay include an engine, a motor, a powertrain, a wheel, a brake, asteering device, etc. The vehicle 100 b may include a sensor unit foracquiring a vehicle state, ambient environment information, userinformation, etc. The vehicle 100 b may generate and transmit the firstinformation/signals to the second wireless device 200 (S10). The firstinformation/signals may include vehicle state information, ambientenvironment information, user information, and etc. The vehicle 100 bmay receive the second information/signals from the second wirelessdevice 200 (S30). The second information/signals may include vehiclestate information, ambient environment information, user information,and etc. The vehicle 100 b may drive on a road, stop, or adjust speed,based on the second information/signals (S50). For example, the vehicle100 b may receive map the second information/signals including data,traffic information data, etc. from an external server (S30). Thevehicle 100 b may generate an autonomous driving path and a driving planbased on the second information/signals, and may move along theautonomous driving path according to the driving plan (e.g.,speed/direction control) (S50). For another example, the control unit orprocessor(s) of the vehicle 100 b may generate a virtual object based onthe map information, traffic information, and vehicle positioninformation obtained through a GPS sensor of the vehicle 100 b and anI/O unit 140 of the vehicle 100 b may display the generated virtualobject in a window in the vehicle 100 b (S50).

In some scenarios, the first wireless device 100 may be an XR device 100c of FIG. 1, which performs the functions, procedures, and/or methodsdescribed in the present disclosure. The XR device 100 c may transmit(S10) and receive (S30) signals (e.g., media data and control signals)to and from external devices such as other wireless devices, hand-helddevices, or media servers, through its communication unit (e.g.communication unit 110 of FIG. 1C). For example, the XR device 100 ctransmits content request information to another device or media server(S10), and download/stream contents such as films or news from anotherdevice or the media server (S30), and generate, output or display an XRobject (e.g. an AR/VR/MR object), based on the secondinformation/signals received wirelessly, through an I/O unit of the XRdevice (S50).

In some scenarios, the first wireless device 100 may be a robot 100 a ofFIG. 1, which performs the functions, procedures, and/or methodsdescribed in the present disclosure. The robot 100 a may be categorizedinto an industrial robot, a medical robot, a household robot, a militaryrobot, etc., according to a used purpose or field. The robot 100 a maytransmit (S10) and receive (S30) signals (e.g., driving information andcontrol signals) to and from external devices such as other wirelessdevices, other robots, or control servers, through its communicationunit (e.g. communication unit 110 of FIG. 1C). The secondinformation/signals may include driving information and control signalsfor the robot 100 a. The control unit or processor(s) of the robot 100 amay control the movement of the robot 100 a based on the secondinformation/signals.

In some scenarios, the first wireless device 100 may be an AI device 400of FIG. 1. The AI device may be implemented by a fixed device or amobile device, such as a TV, a projector, a smartphone, a PC, anotebook, a digital broadcast terminal, a tablet PC, a wearable device,a Set Top Box (STB), a radio, a washing machine, a refrigerator, adigital signage, a robot, a vehicle, etc. The AI device 400 may transmit(S10) and receive (S30) wired/radio signals (e.g., sensor information,user input, learning models, or control signals) to and from externaldevices such as other AI devices (e.g., 100 a, . . . , 100 f, 200, or400 of FIG. 1) or an AI server (e.g., 400 of FIG. 1) usingwired/wireless communication technology. The control unit orprocessor(s) of the AI device 400 may determine at least one feasibleoperation of the AI device 400, based on information which is determinedor generated using a data analysis algorithm or a machine learningalgorithm. The AI device 400 may request that external devices such asother AI devices or AI server provide the AI device 400 with sensorinformation, user input, learning models, control signals and etc.(S10). The AI device 400 may receive second information/signals (e.g.,sensor information, user input, learning models, or control signals)(S30), and the AI device 400 may perform a predicted operation or anoperation determined to be preferred among at least one feasibleoperation based on the second information/signals (S50).

When DRX is configured, the UE monitors PDCCH discontinuously using theDRX operation. For an ON duration in each DRX cycle, the UE is in ActiveTime and monitors PDCCH. If DL data is received during the ON duration,the UE extends the Active Time and monitors PDCCH even after the ONduration.

The extension of the Active Time is done by drx-InactivityTimer, wherethe timer starts at every reception of PDCCH indicating a newtransmission. While the timer is running, the UE is in Active Time andmonitors PDCCH. The UE is also in Active Time based on various timers.

If a carrier aggregation (CA) scheme is configured, the UE configuresmultiple cells, and has to monitor PDCCH on multiple cells. The UEconsumes its power in order to monitor PDCCH. The more the cells the UEneeds to monitor, the more the UE consumes its power.

FIG. 11 shows an example of DRX procedure in the conventional art towhich the carrier aggregation (CA) scheme is applied. In FIG. 11, whenthe UE wakes up, the UE should monitor all cells that are activated.

As the most power consumed in unused serving cell is coming from PDCCHmonitoring, it is necessary to reduce power consumption in CAconfiguration by reducing PDCCH monitoring in unused serving cells.

To reduce power consumption when carrier aggregation (CA) is configured,the present disclosure suggests that the UE should monitor PDCCH on onlyone specific cell among activated cells during an On Duration within aDRX cycle, and should extend PDCCH monitoring on all activated cellsduring Active Time within the DRX cycle if a PDCCH is received on thespecific cell during the On Duration within the DRX cycle.

The UE receives DRX configuration information and CA configurationinformation from the network.

The DRX configuration information includes information of DRX cycle, OnDuration, DRX related timers, etc.

The CA configuration information includes serving cells information thatthe UE needs to configure, and a specific serving cell that the UE needsto monitor PDCCH in each On Duration.

The UE configures at least two serving cells according to the CAconfiguration information, and activates at least two serving cellsamong the at least two serving cells.

Among the configured serving cells, the PCell and PSCell are calledSpecial Cell (SpCell). For Dual Connectivity operation the term SpecialCell refers to the PCell of the MCG or the PSCell of the SCG dependingon if the MAC entity is associated to the MCG or the SCG, respectively.A Special Cell supports PUCCH transmission and contention-based RandomAccess, and is always activated.

The UE also starts DRX operation according to the DRX configurationinformation. For each DRX cycle, there is one On Duration, and the UEmonitors PDCCH transmission opportunity to receive PDCCH during the OnDuration.

In the present disclosure, though multiple serving cells are activated,the UE should monitor the PDCCH during the On Duration only on thespecific serving cell indicated in the CA configuration information.

Alternatively, if the specific serving cell is not indicated in the CAconfiguration information, the UE monitors PDCCH on a pre-definedspecific serving cell, e.g. PCell or PSCell or PUCCH SCell. Thus, it isclear that preferred SCell should be a cell on which a PUCCH is to betransmitted.

If a PDCCH is received on the specific serving cell during the OnDuration, and if the PDCCH indicates a new transmission (DL or UL), theUE starts drx-InactivityTimer and starts to monitor PDCCH on all theactivated serving cells, preferably in the first symbol after the end ofthe PDCCH reception. The UE may stop the drx-onDurationTimer when the UEstarts drx-InactivityTimer.

Once the UE starts to monitor PDCCH on all the activated serving cells,the UE keeps monitoring PDCCH on all the activated serving cells inActive Time of the corresponding DRX cycle. The DRX cycle may be eitherShort DRX cycle or Long DRX cycle.

The Active Time includes the time while:

1) drx-onDurationTimer or drx-InactivityTimer ordrx-RetransmissionTimerDL or drx-RetransmissionTimerUL orra-ContentionResolutionTimer is running; or

2) a Scheduling Request is sent on PUCCH and is pending; or

3) a PDCCH indicating a new transmission addressed to the C-RNTI of theMAC entity has not been received after successful reception of a RandomAccess Response for the Random Access Preamble not selected by the MACentity among the contention-based Random Access Preamble.

Among the Active Time above, the UE monitors PDCCH only on the specificserving cell when only the drx-onDurationTimer is running and no otherActive Time condition is met. Other than the Active Time where only thedrx-onDurationTimer is running, the UE monitors PDCCH on all theactivated serving cells.

For the next DRX cycle, the goes back to the initial state, i.e.,monitors PDCCH during the On Duration only on the specific serving cell.

FIG. 12 shows an example of DRX procedure according to the presentdisclosure.

Referring to FIG. 12, the UE monitor a PDCCH on only cell 1 amongactivated cells (i.e. cells 1-3) during an On Duration within a DRXcycle. Then, if the PDCCH is received on the cell 1 during the OnDuration within the DRX cycle, the UE extends PDCCH monitoring on allactivated cells (i.e. cells 1-3) during Active Time within the DRXcycle. Of course, during the On Duration within a next DRX cycle, the UEmonitors a PDCCH on only cell 1 among activated cells.

In summary, when the MAC entity is in Active Time, if the Active Time isdue to only drx-onDurationTimer running, the MAC entity should monitorthe PDCCH on the SpCell. However, if the Active Time is not due to onlydrx-onDurationTimer running, the MAC entity should monitor the PDCCH onall the activated Serving Cells.

Further, if the PDCCH is received on the SpCell whiledrx-onDurationTimer is running, the MAC entity should stopdrx-onDurationTimer.

The network behavior also follows the invention.

The network transmits PDCCH only on the specific serving cell when theUE is expected to be in On Duration, and transmits PDCCH on any of theactivated serving cells after the UE is expected to receive PDCCHtransmitted on the specific serving cell based on a HARQ feedbackreceived from the UE.

According to the present disclosure, the UE can reduce power consumptionby reducing the number of cells on which the UE monitors PDCCH.

1. A method for receiving a Physical Downlink Control Channel (PDCCH) bya user equipment (UE) in a wireless communication system to which acarrier aggregation scheme is applied, the method comprising: monitoringthe PDCCH during an On Duration within a discontinuous reception (DRX)cycle on a specific serving cell among at least two activated servingcells, and monitoring the PDCCH during an Active Time within the DRXcycle on all of the at least two serving cells based on the PDCCH beingdetected during the On Duration within the DRX cycle on the specificserving cell.
 2. The method of claim 1, wherein all of the at least twoserving cells belongs to a Medium Access Control (MAC) entity.
 3. Themethod of claim 1, wherein the specific serving cell is a cell on whicha Physical Uplink Control Channel (PUCCH) is to be transmitted.
 4. Themethod for claim 1, further comprising monitoring PDCCH during the OnDuration within a next DRX cycle on the specific serving cell
 5. Themethod for claim 1, wherein the PDCCH indicates a downlink reception oran uplink transmission.
 6. A user equipment (UE) in a wirelesscommunication system to which a carrier aggregation scheme is applied,the UE comprising: at least one transceiver; at least one processor; andat least one computer memory operably connectable to the at least oneprocessor and storing instructions that, when executed, cause the atleast one processor to perform operations comprising: monitoring aPhysical Downlink Control Channel (PDCCH) during an On Duration within adiscontinuous reception (DRX) cycle on a specific serving cell among atleast two activated serving cells, and monitoring the PDCCH during anActive Time within the DRX cycle on all of the at least two servingcells based on the PDCCH being detected during the On Duration withinthe DRX cycle on the specific serving cell.
 7. The UE for claim 6,wherein all of the at least two serving cells belongs to a Medium AccessControl (MAC) entity.
 8. The UE for claim 6, wherein the specificserving cell is a cell on which a Physical Uplink Control Channel(PUCCH) is to be transmitted.
 9. The UE for claim 6, wherein theoperations further comprise monitoring PDCCH during the On Durationwithin a next DRX cycle on the specific serving cell.
 10. The UE forclaim 6, wherein the PDCCH indicates a downlink reception or an uplinktransmission.
 11. An apparatus for a user equipment (UE) in a wirelesscommunication system to which a carrier aggregation scheme is applied,the apparatus comprising: at least one processor; and at least onecomputer memory operably connectable to the at least one processor andstoring instructions that, when executed, cause the at least oneprocessor to perform operations comprising: monitoring a PhysicalDownlink Control Channel (PDCCH) during an On Duration within adiscontinuous reception (DRX) cycle on a specific serving cell among atleast two activated serving cells, and monitoring the PDCCH during anActive Time within the DRX cycle on all of the at least two servingcells based on the PDCCH being detected during the On Duration withinthe DRX cycle on the specific serving cell.
 12. A computer readablestorage medium storing at least one computer program comprisinginstructions that, when executed by at least one processor, cause the atleast one processor to perform operations for a user equipment (UE) in awireless communication system to which a carrier aggregation scheme isapplied, the operations comprising: monitoring a Physical DownlinkControl Channel (PDCCH) during an On Duration within a discontinuousreception (DRX) cycle on a specific serving cell among at least twoactivated serving cells, and monitoring the PDCCH during an Active Timewithin the DRX cycle on all of the at least two serving cells based onthe PDCCH being detected during the On Duration within the DRX cycle onthe specific serving cell.